seismic attenuation

This report was prepared as part of a collaboration between the University of Arizona and the Arizona Geological Survey during the initial development of the Arizona Broadband Seismic Network. Although the work is considered “preliminary”, it is the only such work of its kind as attenuation studies for Arizona were non-existent prior to the report’s completion.
The tectonics of Arizona is dominated by the extension in the southern Basin and
Range province, and the transition to the less deformed Colorado Plateau. However,
earthquakes in Arizona tend to be small with most occurring in the northwest part of the
state in the western part of the Colorado Plateau and transition zone. Many of these
earthquakes (magnitudes usually < 4) occur north or south of Grand Canyon indicating
that the western portion of the Colorado Plateau is deforming and not as “stable” as often
described (Kreemer et al., 2010; Brambaugh, 2008). The southern Basin and Range in
Arizona has had few earthquakes over the last century and appears to be less active than
the Nevada or Utah portion of the Basin and Range. However, in 1887 there was a
magnitude 7 earthquake, just south of the Arizona border in Mexico that was widely felt
in southern Arizona (Bull and Pearthree, 1988). The 1887 Great Sonoran Earthquake
produced a sizeable normal fault scarp with up to 4 meters of offset indicating the
southern Basin and Range is capable of significant earthquakes despite the relative low
number of earthquakes presently occurring (Sumner, 1977; see
http://www.geo.arizona.edu/gsat/1887eq/bibliography.html for additional references).
The western part of Arizona is close to Baja and southern California with high rates of
seismicity associated with the San Andreas transform system, hence cities such as Yuma,
could be at risk if a major earthquake occurred on in southern California. Due to the
overall low rates of seismicity there have been few permanent broadband seismic stations
in Arizona until recently and hence, very few studies of earthquakes or seismic
attenuation in Arizona. The NSF funded EarthScope project recently deployed seismic
stations in Arizona for 18 months and the 8 stations that were adopted by the Arizona
State Geological Survey has provided a wealth of data to better characterize the
earthquakes, present day deformation in Arizona, and make preliminary attenuation
measurements for the state (Fig. 1). In order to characterize the present-day deformation
we have determined 21 first motion focal mechanisms for small earthquakes in Arizona.
In addition, we have determined coda Q measurements of attenuation in much of
Arizona.

Publication Date

The maps, reports, and other information and content on this website are provided as a public service for informational purposes only. Accuracy is not guaranteed, and the information contained or linked on this website should not be relied on except as general information. The University makes no warranties or representations of any kind, and specifically disclaims all warranties including the warranty of merchantability and fitness for a particular purpose. Users are responsible for verification of all facts and information to their own satisfaction.